1. Field of the Invention
The present invention pertains broadly to airhouses for supplying conditioned air to the interior of enclosed structures, and more particularly to an improved inlet, damper and burner construction for such airhouses.
2. Description of The Prior Art
Relatively large industrial-type buildings are commonly provided with so-called airhouses for supplying suitably conditioned air to the interior of the building under controlled conditions so as to maintain atmospheric conditions in the building within prescribed parameters of temperature, humidity and air quality, among others. Such units and their integration into systems for maintaining controlled atmospheric conditions within enclosed structures are disclosed and described, for example, in U.S. Pat. Nos. 4,850,264 and 4,960,041, and the above-identified copending patent applications. The disclosures of those patents and copending applications are incorporated herein by reference.
Such airhouses are generally, although not necessarily, located exteriorly of the buildings, as on the roof or around the perimeter thereof, and may include a cabinet comprised of a framework covered with sheet metal housing a burner and a fan or blower. Optionally, they may also include a heat exchanger for cooling purposes and an evaporator for humidifying purposes. The fan draws fresh air from outside the building, as well as return air from the interior of the building. The burner air inlet, outdoor fresh air inlet and return air inlet are provided with adjustable dampers or valves for regulating air flow through their respective passageways. A portion of the fresh air is drawn over the burner or burners to be heated during the heating season, and the remaining fresh air is mixed with building return air in selected proportions. The heated and unheated air merge downstream from the burner and are discharged into the building to maintain the building interior at a desired temperature and pressure. As described in the aforementioned patents and pending applications, a plurality of individual air houses disposed about the structure may be integrated into a network and centrally controlled in an interrelated manner for regulating atmospheric conditions within the structure.
The airhouses utilized heretofore have conventionally included a hooded opening communicating with the outside atmosphere through which air is drawn for both the outside air and burner air inlets, and an opening communicating with the building interior through which building return air is admitted. Each of the outside air and building return air inlets is provided with a louver-type damper wherein the louver elements are adapted to simultaneously pivot about their longitudinal axes to selected angular positions for regulating air flow through the inlets. The airhouses are designed for the blower to operate at a constant velocity and discharge a constant volume of air to the building interior.
The relevant prior art airhouses further have generally been of a so-called 80/20 profile wherein during burner operation a minimum of 20 percent of the incoming air is outside air which is drawn through the burner. In order to maintain the desired pressure within the building, it is thus necessary to modulate the air being admitted to the airhouse, that is, to properly apportion the incoming outside air and building return air. To that end, the outside air damper and the building return air damper are generally interconnected to operate in opposition, that is, as one of the dampers is opened or closed by a particular amount the other is respectively closed or opened by a corresponding amount. For safety purposes the airhouse is designed so that whenever the burner is operable a predetermined minimum proportion, heretofore 20 percent, of the incoming air is outside air which passes through the burner section, while the remaining 80 percent enters through the outside air and building return air dampers.
Louvered dampers may be of either the so-called parallel blade construction or opposed blade construction. In either construction, the angular setting of the blades of the damper between open and closed positions does not bear a straight line relationship with the flow capacity of the damper. For example, opposed blade dampers at a 45.degree. angular setting have only 20 percent of their fully open flow capacity.
Parallel blade dampers at a 45.degree. angular setting have about 90 percent of their fully open flow capacity. As a consequence, opposed positioning of the outside air and building return air dampers to modulate the proportions of the outside and return air drawn into the airhouse results in undesirable wide variations in air velocity through the airhouse.
The fluctuations in velocity, in turn, adversely affect burner operation. Such burners are designed to operate with incoming air passing thereover at a particular velocity, for example, 3000 feet per minute. Fluctuations in the velocity of the air entering the airhouse through the outside air damper and building return air damper affect the velocity of air across the burner, and may result in formation of dangerous combustion gases or lead to automatic shutdown of the burner. More particularly, if the air velocity across the burner is significantly less than the design velocity, incomplete combustion of the gas may occur and result in carbon monoxide formation. If the air velocity significantly exceeds the design velocity, nitrous oxide may be formed and discharged into the building. In addition, when a relatively large difference in velocity is created within the airhouse between the air passing over the burner and the outside air and building return air, a wind shear problem is created, effectively causing a dead space or barrier between the flowing masses of air. As a result, heat transfer from the relatively hotter burner air to the cooler outside and building return air within the airhouse is impeded, and air masses of different temperatures are discharged into the building. Thus, while the prior art direct-fired space heating units or airhouses represent a significant improvement over earlier systems, they have not proven entirely satisfactory in operation.